Effect of Mineral Admixtures and Recycled Concrete on Concrete Compressive Strength

Reducing the quantity of cement used in concrete has been a goal for several years. Mineral admixtures such as silica fume, fly ash and metakaolin are used to replace cement in this research. This research aims to improve concrete compressive strength while becoming greener at the same time. Another aspect is to replace fine and coarse aggregates in concrete with others made of recycled concrete. Experimental tests are conducted by comparing the results of control concrete samples with those where 10% and 15% silica fume and fly ash are used. Metakaolin is utilized by 10%, 15% and 20% by weight of cement. Recycled fine aggregate percentages are 25%,50% and 100% by weight of new fine aggregate. Meanwhile, recycled coarse aggregate percentages are 50% and 100%. From this applied study it is found that the 90-and 28-days optimum percentage of silica fume, fly ash and metakaolin compared to other percentages is 10% which leads to an increase in compressive strength by up to 23%. As for the optimum percentage of recycled concrete coarse and fine aggregates, it is found to be 50% and it corresponds to 33% increase in compressive strength at 90 and 28 days.